User Guide

196 Chapter 10: Events and Messages
on stepFrame
Usage
-- Lingo syntax
on stepFrame
statement(s)
end
// JavaScript syntax
function stepFrame() {
statement(s);
}
Description
System message and event handler; works in script instances in actorList because these are the
only objects that receive
on stepFrame messages. This event handler is executed when the
playhead enters a frame or the Stage is updated.
An
on stepFrame handler is a useful location for Lingo that you want to run frequently for a
specific set of objects. Assign the objects to
actorList when you want Lingo in the on
stepFrame
handler to run; remove the objects from actorList to prevent Lingo from running.
While the objects are in
actorList, the objects’ on stepFrame handlers run each time the
playhead enters a frame or the
updateStage command is issued.
The
stepFrame message is sent before the prepareFrame message.
Assign objects to
actorList so they respond to stepFrame messages. Objects must have an on
stepFrame
handler to use this built-in functionality with actorList.
The
go, play, and updateStage commands are disabled in an on stepFrame handler.
Example
If the child object is assigned to actorList, the on stepFrame handler in this parent script
updates the position of the sprite that is stored in the
mySprite property each time the playhead
enters a frame:
-- Lingo syntax
property mySprite
on new me, theSprite
mySprite = theSprite
return me
end
on stepFrame me
sprite(mySprite).loc = point(random(640),random(480))
end
// JavaScript syntax
// define a constructor class that contains the mySprite property
function Frame(theSprite) {
this.mySprite = theSprite;
}
function stepFrame() {
var myFrame = new Frame(sprite(spriteName).spriteNum);
sprite(myFrame.mySprite).loc = point(random(640),random(480));
end